Polymeric casting materials have gained widespread commercial acceptance during the past decade. As compared to Plaster of Paris casts, the polymeric or so-called "synthetic" casting materials have advantages of being light weight, and strong. Synthetic casting materials are also porous in the hardened state so that the cast is breathable. Typically, orthopedic synthetic casts are made from a curable resin-impregnated narrow fabric or casting tape. The fabric, which is preferably knit, can be formed of glass fibers and/or synthetic fibers such as polyester, nylon, polyolefins and the like.
Polyurethane casting materials which have experienced widespread commercial acceptance are disclosed in Yoon U.S. Pat. 4,433,680. These casting materials employ a water activatable polyurethane prepolymer which contains a dimorpholinodiethylether catalyst. The compositions have a long shelf life during which the polyurethane polymer remains in the liquid state. When the bandage is to be used, it is removed from a sealed package and placed in water for a few seconds. It is removed from the water and applied to the patient usually over a tubular, knitted fabric and a padding. The bandage will set rapidly to a condition where it is capable of immobilizing a fracture.
More recently, colored casting materials have gained widespread commercial acceptance. Coloring of casting materials has been accomplished by adding pigments or dyes to the prepolymer materials as disclosed, for example, in Straube et al. U.S. Pat. No. 4,376,438 and in Klintworth, Jr. U.S. Pat. No. 4,934,356. The pigment and/or dyeing materials added to the prepolymer materials are chosen carefully to avoid causing the prepolymer to gel and/or harden prematurely.
In practice, the colored orthopedic casts are highly desirable to many patients. There are, however, a number of disadvantages associated with the colored casts. In the medical cast room, the colored prepolymers while in the liquid state, can stain tables, floors and other surfaces, causing an undesirable casting room appearance and atmosphere. Similarly, clothing and lab coats of physicians and cast technicians are stained by contact with the colored polymer. In the manufacturing operation, changing from one color prepolymer to another can require cleaning of the coating machinery including removal and cleaning of coating rolls, and flushing of the interior of the coating apparatus.
As colored casting materials have increased in popularity, substantial interest has been expressed for multiple colored and patterned casts. Spirally striped casts have been made by the concurrent winding of two differently colored, separate casting tapes around the fractured limb of the patient. Patterned casts have also been made by forming the main cast body out of a single colored casting material followed by attachment to the surface of the cast, of separate casting materials of different colors which have been precut into desired shapes. A multiple-colored, patterned sleeve for wearing over a cast has also been sold commercially.
Despite the apparent interest in multicolored casts, no practical multicolored casting material has been proposed or previously made available. Physicians and cast technicians have thus only been able to provide multicolored casts by employing several, different colored separate casting bandages in the construction of the cast. In view of the demands on the time and skill of the medical personnel, multicolored casting materials are thus not practically available.